I. Field of the Invention
The present invention relates to a passive system and corresponding methods for efficiently and economically determining which of a plurality of possible target locations are, in fact, real target locations.
II. Description of the Prior Art
Passive surveillance systems are known which can identify the bearing or azimuth of a target by simply rotating a receiving antenna and determining the azimuth angle of that antenna upon receipt of a signal transmitted by the target. The bearing or "strobe" of each target may be displayed and these bearings or strobes can be transmitted or cross-told to a cooperating system. With the bearings or strobes from a cooperating system the resultant display may form a crisscross pattern and the targets under consideration may actually be positioned at any one of the intersections.
The locations of the intersections are accurately defined by a known triangulation method, using the bearing or "strobe" angle measured by each surveillance system and using the known distance between the surveillance systems.
The number of intersections of such a display is the square of the targets detected. Accordingly, if as shown in FIG. 1 there were a first receiver R1 which detects N (for example 3) targets, each at an azimuth bearing A.sub.R1N, and there were provided a distance S from the first receiver R1 a second receiver R2 which was in range of the same three targets and received signals from each of those targets at a corresponding azimuth angle A.sub.R2N, the resultant cross-pattern would produce nine possible target locations 1.sub.1 -1.sub.9.
At present, no quick way exists to determine which of the possible target locations is an actual location, although software programs to track target intersections, to analyze their movements, and to apply logic to accomplish the deghosting or actual target location function does exist. Such systems are moderately successful in that they may be able to eliminate a certain percentage of the possible target locations as being actual target locations. However, such systems have an inherent limitation because of the requirement that the depression angle of the antenna at the time of receipt of a signal be physically measured. Due to limited vertical aperture, weight, and aerodynamic considerations associated with airborne systems physical, measurement of such depression angles cannot be accomplished with the necessary accuracy so as to confidently determine those possible target locations which are, in fact, real.
Accordingly, it is an object of the subject invention to provide a passive surveillance system which can efficiently and effectively identify which of a plurality of possible target locations is, in fact, a real target location.
Additional objects and advantages of the invention will be set forth in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.